linux-kernel - Re: [patch 2/2] enables booting a NUMA system where some nodes have no memory

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Message-ID: <20061116013534.GB1066@sgi.com>
Date:	Wed, 15 Nov 2006 19:35:34 -0600
From:	Jack Steiner <steiner@....com>
To:	Christoph Lameter <clameter@....com>
Cc:	Christian Krafft <krafft@...ibm.com>, linux-mm@...ck.org,
	Martin Bligh <mbligh@...igh.org>, linux-kernel@...r.kernel.org
Subject: Re: [patch 2/2] enables booting a NUMA system where some nodes have no memory

On Wed, Nov 15, 2006 at 02:40:36PM -0800, Christoph Lameter wrote:
> On Wed, 15 Nov 2006, Jack Steiner wrote:
> 
> > A lot of the core infrastructure is currently missing that is required
> > to describe IO nodes as regular nodes, but in principle, I don't
> > see anything wrong with nodes w/o memory.
> 
> Every processor has a local node on which it runs. The kernel places 
> memory used by the processor on the local node. Even if we allow
> nodes without memory: We still need to associate a "local" node to the 
> processor. If that is across some NUMA interlink then it is going to be 
> slower but it will work.

True.

> 
> AFAIK It seems to be better to explicitly associate a memory node with a 
> processor during bootup in arch code. 
> 
> Various kernel optimizations rely on local memory. Would we create 
> a  special case here of a pglist_data structure without a zones structure? 
> 
> It seems that the contents of pglist_data are targeted to a memory node. 
> If we do not have a pglist_data structure then the node would not exist 
> for the kernel.
> 
> What would the benefit or difference be of having nodes without memory?

I doubt that there is a demand for systems with memoryless nodes. However, if the
DIMM(s) on a node fails, I think the system may perform better
with the cpus on the node enabled than it will if they have to be
disabled.



-- jack
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